sblock Elements - Result Question 20
####17. $MgSO _4$ on reaction with $NH _4 OH$ and $Na _2 HPO _4$ forms a white crystalline precipitate. What is its formula? $(2006,3 M)$
(a) $Mg\left(NH _4\right) PO _4$
(c) $MgCl _2 \cdot MgSO _4$
(b) $Mg _3\left(PO _4\right) _3$
(d) $MgSO _4$
(1993, 1M)
(a) $Cs$
(b) $Si$
(c) $Sn$
(d) $Ti$
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Answer:
Correct Answer: 17. (a)
Solution:
- Temporary hardness of water is due to presence of soluble $Ca\left(HCO _3\right) _2$ or $Mg\left(HCO _3\right) _2$.
Permanent hardness of water is due to the presence of $CaCl _2$ or $CaSO _4$ or $MgCl _2$ or $MgSO _4$.
Temporary hardness of water is also called carbonate hardness which can be easily removed by boiling or by treatment with $Ca(OH) _2$ (Clark’s method).
